Fault indicator



S. LU BKIN FAULT INDICATOR Filed Dec.

Sept 6, 1955 D- C VOLTAGE SOURCE LOAD //V [/5 N TOR.

SAMUEL L UB/(IN D-C VO LTAGEl 2 SOURCE iZ0 Relay Coil United States Patent FAULT INDICATOR Samuel Lubkin, Brooklyn, N. Y., assignor to Underwood Corporation, New York, N. Y., a corporation of Delaware Application December 31, 1953, Serial No. 401,559

9 Claims. (Cl. 340250) This invention relates to electrical apparatus, and more particularly to means for indicating the occurrence of a fault in electrical circuits.

Electrical circuits are commonly protected by fuses against faults which occur in associated apparatus. A common electrical fuse is simply an electrical conductor having a weak section which burns out when excessive electrical current is drawn through the fuse when a fault occurs.

A more complex fuse is the type which not only burns out as a result of excessive current but which also includes a movable mechanical link which is actuated when the fuse is blown. The movable or moving-link fuse is frequently used in circuits in association with a voltage source so that, when excessive current is drawn through the fuse, the moving link activates a fault indicator circuit which may be, for example, an alarm or a shutdown control circuit.

One method by which the moving-link fuse is used to initiate the operation of a fault indicator circuit is to connect the protected voltage source to the movable link so that, when the fuse burns out, the voltage is connected to the indicator circuit which is thereby rendered operative. However, when moving-link fuses are used to protect voltage sources which supply differentmagnitudes of voltages, the indicator circuit must be adjusted to be operative when any of the supply voltages are connected to it. This requirement severely complicates the design of the indicator circuit so that the employment of this method is of questionable value as a practical matter.

It is accordingly an object of the invention to provide an improved fault-indicating apparatus.

Another object of the invention is to provide an inexpensive fault indicator circuit for use with a plurality of voltage sources having different supply voltages.

A further object of the invention is to provide an improved fuse apparatus which employs moving-link fuses to indicate the occurrence of a fault in associated circuits.

Briefly, a preferred embodiment of the invention comprises a moving-link fuse connected in series between each voltage source to be protected and its associated load circuit. Each moving link is arranged to contact a common conductor when actuated by the blowing of the fuse and to thereby complete a secondary alternatingcurrent circuit which indicates the occurrence of a fault.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawing, in which the sole figure shows a schematic diagram of a preferred embodiment of the invention, which illustrates the principle of the invention and the best mode which has been contemplated of applying that principle.

In the fault indicator apparatus shown in the figure, the DC. voltage supply sources and 12, which can supply different magnitudes of voltage, are coupled respectively via the fuses 2 and 4 to the loads A and B.

The fuses 2 and 4 are both of the movable link type.

Patented Sept. 6, 1955 "ice Fuse 2, for example, has an apertured end receiving a movable link 6. The movable link 6 comprises the fusible Wire 7, which extends through the aperture, and the head 11. The movable link 6 is urged outwardly by a spring 9a when the fusible wire 7 breaks due to excessive electrical heating causing the fuse 2 to blow. Excessive electrical heating is caused by excessive current passing through the fusible wire 7.

Each of the fuses 2 and 4 in a working embodiment of the invention is a Buss fuse. The invention canalso utilize analogous overload devices such as grasshopper fuses or circuit breakers providing some part of these devices can be adapted to simulate the function of the movable link 6.

The fuses 2 and 4 are mounted in the clips 16a16b and 16c-16d respectively. The fuse clip 16b-is coupled to the load A so that the DC. voltage source 10 supplies power through the fuse 2 for the load A. The fuse clip 16b is connected to ground via the capacitor 22.

The D.-C. voltage source 12 is coupled via the fuse 4 to load B and supplies the power for the load B. The fuse clip is coupled to ground by means of the capacitor 24.

For convenience in hereinafter explaining the operation of the invention, the movable link 8 of the fuse 4 is shown as fused or burned through as a result of excessive current being drawn from the D.-C. voltage source 12.

The movable link 6 is coupled to ground via the apertured end of the fuse 2, the clip 16b, and the capacitor 22. More particularly, the movable link 6 is connected to the apertured end of the fuse 2 by the spring 9a and by the direct contact of the movable link 6 with the apertured end. The coupling to ground of the movable link 6 by the capacitor 22 is maintained when the fusible wire 7 is broken and the movable link 6 urged outwardly. The movable link 8 is coupled to ground via the capacitor 24 in a similar manner.

A rod or bus 14 is positioned adjacent to the fuse clips 16 such that when one of the fuses 2 or 4 blows, the corresponding movable link 6 or 8 is sprung outward and makes contact with the bus 14.

The bus 14 is connected to the A.-C. source 18 via the relay coil 20. The relay coil 20 in a working embodiment of the invention is a ten volt coil of a Struthers Dunn Relay Type 29 XAX (not shown). The relay is an example of one type of indicator which may be used in the indicator circuit and can be replaced by other types of utilization means, for example, bells or lamps.

The A.-C. source 15: supplies the power for the relay coil 2% which is in series with the movable link 3 (shown in contact with the bus 14) and the capacitor 24. The capacitor 24 not only completes the indicator circuit for the A.-C. source 18 but also functions to isolate the A.-C. source 18 from the load B. In a working embodiment of the invention, the capacitors 22 and 24 are two micro-farad capacitors.

All of the voltage sources and the loads are assumed to be connected to a common reference point; for example, ground.

The operation of the invention will be described in connection with a fault in load B causing excessive current to flow through and blow the fuse 4.

When fuse 4 blows, the movable link 3 is urged outwardly by the spring Q5 and contacts the bus 14 to complete the indicator circuit through the relay coil 20, thereby actuating the associated relay.

The indicator circuit comprises the A.-C. source 18, the relay coil 2%, the bus 14, the movable link 8 and the capacitor 24 in series. Current flows from the A.-C. source 18 to ground via the capacitor 24.

it should be noted that the capacitor 24 bypasses the current to ground thus protecting the load B. If the fuse 2 should blow instead of the fuse 4, the relay coil 20 would be energized in a similar manner.

Therefore, the energization of the relay coil 20 is completely independent of the magnitudes of the voltages of the protected D.-C. voltage sources it) and 12 since only the magnitude of the voltage of the A.-C. source 18 is significant in the indicator circuit.

In another embodiment of the invention, a fault indicator circuit is provided for operation in conjunction with protected A.-C. voltage sources. Thus, if the D.-C. voltage sources 10 and 12 in the figure are replaced by A.-C. voltage sources, the A.-C. source 18 can be made a D.-C. source which will operate an appropriate indicator. The capacitors 22 and 24 are then replaced by suitable inductors. The non-grounded ends of the inductors are respectively connected to the loads A and B via suitable capacitors which isolate the D.-C. indicator power source from the loads. In this embodiment, the protected A.-C. voltage sources are capacitively coupled to the load B.

In a further embodiment of the invention, all of the protected voltage sources, as well as the indicator power source, are A.-C. voltage sources. If the DC. voltage sources 10 and 12 in the figure are accordingly protected A.-C. voltage sources which supply voltages of different magnitudes at a given frequenc the indicator power source is chosen to have a different frequency. The capacitors 22 and 24 are then replaced by suitable combinations of filters so that when a fuse blows, the power indicator source is isolated from the loads by virtue of the filters. Thus the invention may be utilized in conjunction with voltage sources which are all of the A.-C. type.

In still other embodiments of the invention, the connections to the fuses 2 and 4 may be reversed with suitable modification of previously described circuits.

In summary, in accordance with the invention, relatively simple and inexpensive fault indicator circuits are provided which indicate the occurrence of an overload on any of a plurality of protected power sources. Further, these protected power sources may be A.-C. or D.-C. and may supply voltages of difierent magnitudes.

There will now be obvious to those skilled in the art many modifications and variations utilizing the principles set forth and realizing many or all of the objects and advantages of the embodiments described but which do not depart essentially from the spirit of the invention.

What is claimed is:

1. In electrical apparatus for indicating the occurrence of a fault which causes an overload on one of a plurality of voltage sources supplying difierent voltages to associated loads, an indicator, a power source for feeding said indicator, a plurality of fuses, each of said fuses having a movable link and means for displacing said movable link when a fault occurs, each of said fuses being associated with one of said voltage sources, and an impeder for completing an indicator circuit, said indicator circuit including said power source, said indicator, said impeder and said movable link in series when a fault occurs, said impeder bypassing the indicator power current by the associated load when a fault occurs.

2. Apparatus for indicating the occurrence of a fault in any of a plurality of direct-current voltage supply sources which supply different voltages to associated power utilization circuits comprising an indicator, an alternating-current source for feeding said indicator, a plurality of fuses, each of said fuses having a movable link and means for displacing said movable link when a fault occurs, each of said fuses being associated with one of said direct-current voltage supply sources and with an associated power utilization circuit, and a capacitor associated with each of said direct-current voltage sources for completing an indicator circuit when one of said fuses is blown, said indicator circuit including said alternating-current source, said indicator, said movable link, and said capacitor in series, said capacitor electrically bypassing said alternating-current by said associated power utilization circuit.

3. Apparatus for indicating the occurrence of an overload of an associated power source connected to a power utilization circuit comprising a power overload device in series with said power utilization circuit, said power overload device having a movable link which is moved when said power overload device is actuated, an indicator, an indicator power source for supplying power to said indicator, said power overload device being arranged such that upon the occurrence of a fault in said utilization circuit said movable link is moved to complete an indicator circuit, and means for electrically isolating said indicator circuit from said power utilization circuit before and after the occurrence of said fault.

4. Apparatus for indicating the occurrence of an overload on any of a plurality of direct-current power sources connected to associated direct-current power utilization circuits comprising a power overload device in series with each of said direct-current power utilization circuits, each of said power overload devices having a movable link which is moved when said power overload device is actuated, an indicator, an alternatingcurrent indicator power source for supplying alternatingcurrent power to said indicator, each of said power overload devices being arranged such that upon the occurrence of an overload said movable link is moved to complete an indicator circuit, and means including a capacitor for electrically isolating said indicator circuit from said direct-current power utilization circuit before and after the occurrence of said fault.

5. Apparatus for indicating the occurrence of an overload on an associated direct-current power source connected to a power utilization circuit comprising a power overload device in series with said power utilization circuit, said power overload device having a movable link which is moved when said power overload device is actuated, an indicator, an alternating-current power source for applying alternating-current power to said indicator, said power overload device being arranged such that upon the occurrence of an overload said movable link is moved to complete an alternating-current indicator circuit, and capacitor means for electrically isolating said alternating-current indicator circuit from said power utilization circuit after the occurrence of said fault.

6. Apparatus for indicating the occurrence of an overload on any of a plurality of direct-current power sources each connected to an associated direct-current power utilization circuit comprising a fuse in series with each of said direct-current power utilization circuits, each of said fuses having a fusible element and means for displacing one end of said fusible element in response to fusion thereof, an indicator, an alternating-current indicator power source for supplying alternating-current power to said indicator, each of said fuses being arranged such that upon the occurrence of a fault in said associated direct-current power utilization circuit one end of said fusible element is displaced to complete an alter mating-current fault indicator circuit, and capacitor means for electrically isolating said alternating-current fault indicator circuit from said direct-current power utilization circuit after the occurrence of said fault.

7. A fuse circuit comprising a plurality of voltage sources for providing currents and voltages, a plurality of loads, a plurality of fuses for passing current to said loads from said voltage sources, said fuses having movable links, a bus, one of said movable links contacting said bus when the current passing through the associated one of said fuses is excessive, said fuse decoupling the associated one of said loads from said voltage source, a utilization means, an alternating-current source for feeding said utilization means, said utilization means being coupled to said bus, and a plurality of capacitors coupling said movable links to ground, the one of said capacitors associated with the one of said movable links which contacts said bus completing a circuit for said alternating-current source and preventing said alternatingcurrent source from feeding any of said plurality of loads.

8. Apparatus for indicating the occurrence of an overload on an associated direct-current power source connected to a power utilization circuit comprising a power overload device in series with said power utilization circuit, said power overload device having a movable member which is moved when said power overload device is actuated, an indicator, an alternating-current power source for supplying alternating-current power to said indicator, said power overload device being arranged such that upon the occurrence of an overload said movable member is moved to complete an alternating-current indicator circuit, and capacitor means for bypassing said alternating-current by said power utilization circuit after the occurrence of said fault.

9. In electrical apparatus for indicating the occurrence of a fault which causes an overload on one of a plurality of voltage sources supplying different voltages to associated loads, an indicator, a power source for feeding said indicator, a plurality of power overload devices, each of said power overload devices having a movable member and means for displacing said movable member when a fault occurs, each of said power overload devices being associated with one of said voltage sources, and an impeder for completing an indicator circuit, said indicator circuit including said power source, said indicator, said impeder and said movable member when a fault occurs, said impeder bypassing the indicator power current by the associated load when a fault occurs.

References Cited in the file of this patent UNlTED STATES PATENTS 2,405,429 Wald Aug. 13, 1946 2,464,848 Collins Mar. 22, 1949 2,476,236 Buckley July 12, 1949 

